1. Field of the Invention
The invention relates both to a system for measuring electric power supplied through a power distribution network and, inter alia, detecting theft of power from the network, and to a remote reading Hall effect based electric power meter for use therein.
2. Description of the Prior Art
Over the past decade, fuel supplies, particularly crude oil, have become increasingly scarce and consequently have sharply escalated in price. Of necessity, electric utilities, particularly those dependent on oil, have often attempted to increase their prices to all their customers in an attempt to recover the increased cost of fuel. However, electric utilities have come under substantial pressure from both consumer groups and regulatory authorities to adequately justify each increase. More often than not, these utilities have been allowed to increase their prices far less than they originally requested. As a result, electric utilities find themselves under significant economic pressure to reduce their costs in order both to meet current expenses and to maintain their profits at an appropriate level sufficient to attract new sources of investment capital. Reducing costs often entails finding and exploiting economies in all areas of power generation, including but not limited to obtaining economical fuel sources. For example, as discussed in detail below, significant economies can be obtained in metering.
Electric power is supplied to every customer by wire, i.e. over power lines. Owing to the losses inherent in this supply process, a meter must be placed at the location of each customer site to measure the amount of electric power consumed there. At present, such a power meter comprises a relatively large electro-mechanical device which generally employs a disk that rotates at a speed proportional to the simultaneous power consumption. This disk is, in turn, mechanically coupled to a counter, visible on the face of the meter, which continuously totalizes the number of times the disk rotates. The value displayed at any instant is the meter "reading" and it represents the total amount of power measured by the meter since it was first placed in service. In order to bill each customer for the amount of power it consumes during any given period, a utility must first read the meter existing at the site of that customer and then subtract the meter reading occurring at the beginning from that occurring at the end of the period. At present, generally all utilities read their meters manually. In other words, a human meter reader visits each customer site and records the reading on each meter situated there. These readings are then brought back to a central location where they are then manually entered into a computer or other data processing equipment which generates customer bills.
Such a metering system possesses two major drawbacks -- the meter itself and the manner in which it is read, both of which result in significant expense for a utility.
First, regarding the meter itself, electro-mechanical rotating disk type meters are expensive devices and, in certain instances, somewhat inaccurate. Although these meters are quite reliable and possess a rather long useful lifetime, often stretching to 20 to 30 years, their acquisition cost is high, generally running to $500 or more per meter. In addition, the rotating disk assembly and the inter-connected counter possess a certain amount of mechanical inertia which slows the response of the meter. This, in turn, often prevents the meter from quickly reacting to load changes which result in short term increases (often lasting less than a second and commonally referred to as "surges") in consumption. Consequently, these meters might react somewhat to a relatively long lasting surge but more likely, since most surges are relatively short, will completely ignore it. Inasmuch as most electric utilities supply huge numbers of consumers, any one of which can momentarily consume a sizable amount of power in a surge, a utility loses significant amounts of revenue by not measuring the power consumed by all its customers during surges and charging for this power. To account for this loss, some utilities might assume, that a certain amount of power will be consumed during surges, and accordingly adjust their rates upward to recover what would otherwise be totally lost revenues. However, these utilities have no accurate way of checking their assumptions against actual consumption patterns to validate and/or correct these assumptions in order to minimize their lost revenue.
Furthermore, with the price of electricity steadily rising, a large and increasing amount of electricity is being stolen from the power lines. Since each customer has access to its incoming electrical wiring, it is relatively easy for anyone to wire around (by-pass) a meter and hence receive unmeasured power. Inasmuch as theft of electrical power is now a crime in most, if not all, jurisdictions thereby slowing, at least hopefully, the growth of this crime, stolen power still accounts for significant lost utility revenues. With the present manually read metering system, utilities must wait until after they have processed the meter readings taken at the end of a measurement period in order to determine measurement discrepancies indicative of theft. Unfortunately, the time lag, occurring between the time theft occurs and the time this theft is finally detected, is often too long to prevent the utility from taking quick corrective action to minimize its lost revenue. Oftentimes, sophisticated thieves may steal power at certain selected times or for certain selected intervals in order to disguise their meter readings and thereby avoid detection either completely or for prolonged periods, hence depriving the utility of long term revenues.
Now, second, apart from the meter itself, manual meter reading is a very slow, labor intensive process which is inordinately expensive. A skilled meter reader may be able to read anywhere from typically 20 to 100 meters a day depending upon where the meters are situated. The rate might be far less in a rural community where individual meters are geographically separated by wide distances and more in a typical city where many meters are often clustered together in one location. Since a typical utility might supply hundreds of thousands of separate customer sites and read each meter once every month or two, a utility must employ a significant number of meter readers. Moreover, the utility not only incurs the salary expense of a meter reader, but also the expense of providing and maintaining a vehicle for each meter reader to use. All these expenses often reach staggering proportions in fairly short periods of time and are always factored into the electric rate(s) charged by a utility.
It has been widely known for some time that use of a widespread automated power metering system employing relatively inexpensive, responsive, accurate and highly reliable meters which telemeter data back to a central location can yield substantial cost savings over the electro-mechanically based manually read metering systems in use today by most, if not all, of the electric utilities in the country. These automated systems are commonly referred to as "remote meter reading" systems. Unfortunately, while many such systems have been proposed, none has seen commercial use. For example, several systems, typified by that disclosed in U.S. Pat. No. 4,241,237 (issued to Paraskevakos et al on Dec. 23, 1980), rely on transmitting each meter reading over the telephone network to a central location for processing and hence require that each meter be connected to a telephone line thereby disadvantageously adding significant expense to the overall metering system. Other systems--typified by that disclosed in U.S. Pat. No. 4,350,980 (issued to Ward on Sept. 21, 1982); U.S. Pat. No. 3,656,112 (issued to Paull on Apr. 11, 1972) and U.S. Pat. No. 3,264,633 (issued to Hellar on Aug. 2, 1966)--rely on using the power line frequency as the carrier medium. By using the existing power network as both the source of electric power and the carrier medium, this method of transmitting data advantageously eliminates the need for a separate network, such as telephone, to carry the meter readings to a central location and hence significantly minimizes expense. However, these power line communication based metering systems known to the art all rely on using rotating disk meters which, as noted above, are expensive to purchase and slow to respond. Consequently, these systems fail to accurately measure surges. Hence, while these systems would certainly provide some economies over prior art manually read metering systems, these power line communication based metering systems known to the art fail to produce maximum cost savings to a utility. Moreover, none of these known remote meter reading systems, whether using power line communication or not, can readily detect power theft.